EP1708553B1

EP1708553B1 - Lead mounting method

Info

Publication number: EP1708553B1
Application number: EP05113090A
Authority: EP
Inventors: Itaru Mitsumi Electric Co. Ltd. Takeda; Tomoyuki Mitsumi Electric Co. Ltd. Kato; Yasuo Mitsumi Electric Co. Ltd. Shoji
Original assignee: Mitsumi Electric Co Ltd
Current assignee: Mitsumi Electric Co Ltd
Priority date: 2005-03-28
Filing date: 2005-12-30
Publication date: 2012-10-03
Anticipated expiration: 2025-12-30
Also published as: EP1708553A2; US20090072008A1; US8305768B2; JP2006277970A; EP1708553A3; JP4877455B2; US20060215376A1

Description

Backaround of the Invention:

This invention relates to a secondary battery protecting module having a protection circuit for protecting a chargeable battery (secondary battery) such as a lithium ion battery and, in particular, to a method of mounting a lead to be connected to a terminal, such as a terminal of a secondary battery, to a printed board.
Among various secondary batteries, in particular, a lithium ion battery is easily damaged by overdischarge and overcharge. It is therefore essential and indispensable to provide a secondary battery protection circuit for detecting an overdisharged state and an overcharged state of the lithium ion battery as a secondary battery to protect the secondary battery from the overdischarged state and the overcharged state. The secondary battery protection circuit comprises an overdischarge preventing mechanism and an overcharge preventing mechanism. For example, the secondary battery protection circuit is disclosed in Japanese Patent (JP-B) No. 2872365 or Japanese Unexamined Patent Application Publication (JP-A) No. 2001-169477 . Typically, an IC chip (protection IC) is used as the secondary battery protection circuit.
The above-mentioned secondary battery protection circuit (protection IC) is disposed on a printed board (circuit board) (for example, see Japanese Unexamined Patent Application Publication (JP-A) No. 2001-268808 ). On the printed board, a power MOSFET (power IC) serving as a discharge control switch and a charge control switch, and a plurality of electronic components, such as a resistor and a capacitor, are disposed. A combination of the printed board, the secondary battery protection circuit, the power MOSFET, and the electronic components is called a secondary battery protection module.
The secondary battery protection module is electrically connected to terminals of the secondary battery such as the lithium ion battery. A combination of the secondary battery protection module and the secondary battery is called a battery pack.
The secondary battery has an anode terminal and a cathode terminal as the terminals. In order to establish electrical connection with the anode terminal and the cathode terminal of the secondary battery, the secondary battery protection module has a pair of leads on the printed board. For example, each lead comprises a nickel lead. One of the leads which is to be connected to the anode terminal of the secondary battery is called an anode lead. The other lead to be connected to the cathode terminal of the secondary battery is called a cathode lead.
On the other hand, in order to establish electrical connection with a load or a battery charger, the secondary battery protection module has a pair of external connection terminals on the printed board. One of the external connection terminals is a positive terminal. The other external connection terminal is a negative terminal.
Referring to Fig. 1, a related secondary battery protection module 10A will be described. The secondary battery protection module 10A comprises the printed board (circuit board) 11 having a principal surface 11a and a back surface 11b opposite to each other. On the principal surface 11a of the printed board 11, the secondary battery protection circuit (protection IC), the power MOSFET (power IC), the electronic components, and the leads (the anode lead and the cathode lead) 21A (only the anode lead being illustrated in Fig. 1) are disposed. On the other hand, on the back surface 11b of the printed board 11, the external connection terminals (the positive terminal and the negative terminal) and so on are disposed. Between the anode lead 21A and the cathode lead, the secondary battery protection circuit (protection IC) is connected through an internal wiring of the printed board 11. Between the cathode lead and the negative terminal, the power MOSFET (power IC) is connected through another internal wiring of the printed board.
As shown in Fig. 1, each of the leads 21A to be connected to the a node terminal and the cathode terminal of the secondary battery has an L shape. Specifically, the L-shaped lead 21A has a mounted part 21Aa to be mounted (or disposed) on the principal surface 11a of the printed board 11 and a connected part 21Ab to be connected to the terminal (the anode terminal or the cathode terminal) of the secondary battery.
In the secondary battery protection module 10A, the L-shaped lead 21A is mounted on the principal surface 11 a of the printed board 11 in the following manner. It is noted here that, on the principal surface 11a of the printed board 11, a land 50 is formed. At first, a flat lead is prepared. The mounted part 21Aa of the flat lead is connected and fixed to the land 50 of the principal surface 11a of the printed board 11 by using a solder 52. Thereafter, the connected part 21Ab of the flat lead is bent by 90° (right angle) with respect to the mounted part 21Aa. Thus, the flat lead is formed into the L-shaped lead 21 A.
As described above, in the secondary battery protection module 10A, the lead is mounted on the principal surface 11a of the printed board 11 by connecting and fixing the flat lead to the land 50 of the principal surface 11a of the printed board 11 using the solder 52 and thereafter bending the flat lead by 90° to form the flat lead into the L-shaped lead 21 A.
In the above-mentioned lead mounting method, when the flat lead is bent by 90°, a crack may be caused to occur in the solder 52. In order to avoid occurrence of the crack, the flat lead is bent at a position spaced by a predetermined distance from an edge of the land 50 as shown in Fig. 1. Therefore, the mounted part 21Aa has a length Lm' greater than a length LI of the land 50 in a bending direction.
However, even if the flat lead is bent at the position spaced from the edge of the land 50, the solder 52 is subjected to a force in a direction of separating the solder 52 from the land 50. As a result, it is difficult to completely avoid occurrence of the crack in the solder 52.
US20030034169A discloses a flat conductor strip for connecting a circuit board substrate to a rechargeable battery cell wherein the conductor strip includes cut-out portions. The flat conductor strip is soldered to the circuit board and then bent about the cut-out portions; the cut-out portions increasing the peel strength of the conductor strip from the circuit board.
EP1403942A discloses a battery pack including a cell connected to a circuit substrate by an L-shaped lead plate, the circuit substrate including external battery pack terminals.
It is therefore an object of this invention to provide a lead mounting method capable of completely avoiding occurrence of a crack in a soldering portion.
It is another object of this invention to provide a secondary battery protection module having a lead mounted by the method.
The invention consists in a lead mounting method of mounting, onto a principal surface of a printed board, a lead adapted to be connected to a terminal, characterized in that said method comprises the steps of:

preparing a flat lead which has a mounted part having a lower surface to be disposed on the principal surface of said printed board and a connected part to be connected to said terminal;
bending said flat lead into an L-shape so that said mounted part and said connected part are perpendicular to each other to obtain an L-shaped lead; and
connecting and fixing the entire lower surface of the mounted part of said L-shaped lead to a land formed on the principal surface of said printed board by soldering so that the mounted part of said L-shaped lead has a length in a bending direction slightly less than a length of the land and so as to form a fillet of the soldering in order to firmly attach the lead on the land,

In this invention, the flat lead is preliminarily formed into an L shape and thereafter mounted onto the principal surface of the printed board by soldering. It is therefore possible to completely avoid occurrence of a crack in a soldering portion.

Brief Description of the Drawings

Fig. 1 is a sectional view of a related secondary battery protection module;
Figs. 2A to 2D show a secondary battery protection module to which a lead mounting method according to an embodiment of this invention is applicable, Fig. 2A being a plan view, Fig. 2B being a rear view, Fig. 2C being a front view, Fig. 2D being a side view; and
Fig. 3 is a sectional view of the secondary battery protection module illustrated in Figs. 2A to 2D.

Description of the Preferred Embodiment

Now, an embodiment of this invention will be described in detail with reference to the drawing.
Referring to Figs. 2A to 2D, description will be made of a secondary battery protection module 10 to which a lead mounting method according to the embodiment of this invention is applicable.
As will later be described, the secondary battery protection module 10 is electrically connected to a secondary battery (not shown) such as a lithium ion battery. The secondary battery has an anode terminal and a cathode terminal. A combination of the secondary battery protection module 10 and the secondary battery is called a battery pack.
The secondary battery protection module 10 comprises a printed board 11. The printed board 11 has a principal surface 11 a and a back surface 11 b opposite to each other.
The printed board 11 illustrated in the figure has a thickness of about 0.7 mm.
On the principal surface 11a of the printed board 11, a secondary battery protection circuit (protection IC) 12, a power MOSFET (power IC) 13 serving as a discharge control switch and a charge control switch, a plurality of electronic components 14 such as a resistor and a capacitor are disposed.
The secondary battery protection circuit 12 is a circuit for detecting an overdischarged state and an overcharged state of the secondary battery to protect the secondary battery from the overdischarged state and the overcharged state. The power MOSFET 13 serves as a switching member for turning on and off discharge and charge of the secondary battery under control of the secondary battery protection circuit 12.
In order to establish electrical connection with the anode terminal and the cathode terminal of the secondary battery, the secondary battery protection module 10 has a pair of leads 21 and 22 on the principal surface 11a of the printed board 11. For example, each of the leads 21 and 22 comprises a nickel lead containing 99% of a nickel component. One lead 21 to be connected to the anode terminal of the secondary battery is called an anode lead while the other lead 22 to be connected to the cathode terminal of the secondary battery is called a cathode lead.
On the other hand, as illustrated in Fig. 2B, in order to establish electrical connection with a lead or a battery charger, the secondary battery protection module 10 has a pair of external connection terminals 31 and 32 on the back surface 11 b of the printed board 11. One of the external connection terminals is a positive terminal 31 and the other is a negative terminal 32. Each of the positive terminal 31 and the negative terminal 32 is plated with gold and has a thickness greater than 0.5 µm.
Between the anode lead 21 and the cathode lead 22, the secondary battery protection circuit (protection IC) 12 is connected through an internal wiring (not shown) of the printed board 11. Between the cathode lead 22 and the negative terminal 32, the power MOSFET (power IC) 13 is connected through another internal wiring (not shown) of the printed board 11.
As illustrated in Fig. 2D, each of the leads 21 and 22 to be connected to the anode terminal and the cathode terminal of the secondary battery has an L shape. Specifically, the L-shaped lead 21 has a mounted part 21a to be mounted (disposed) on the principal surface 11a of the printed board 11 and a connected part 21 b to be connected to the anode terminal of the secondary battery. Likewise, the L-shaped lead 22 has a mounted part 22a to be mounted (disposed) on the principal surface 11a of the printed board 11 and a connected part 22b to be connected to the cathode terminal of the secondary battery.
Those circuit components mounted on the principal surface 11a of the printed board 11, i.e., the secondary battery protection circuit 12, the power MOSFET 13, and the electronic components 14 are encapsulated by a resin 40.
Next referring to Fig. 3 in addition to Figs. 2A to 2D, description will be mad e of a lead mounting method of mounting the L-shaped leads 21 and 22 onto the principal surface 11a of the printed board 11 according to the embodiment. On the principal surface 11a of the printed board 11, a land 50 is formed. In Fig. 3, the anode lead 21 alone is shown in an enlarged scale. As will readily be understood, the cathode lead 22 is similar in structure.
At first, two flat leads are prepared. Next, the two flat leads are bent into an L shape so that the mounted parts 21a and 22a to be disposed on the principal surface 11a of the printed board 11 are perpendicular to the connected parts 21b and 22b to be connected to the terminals (the anode terminal and the cathode terminal) of the secondary battery. Thus, the L-shaped leads 21 and 22 are obtained. The mounted parts 21a and 22a of the L-shaped leads 21 and 22 are connected and fixed onto the land 50 of the principal surface 11a of the printed board 11 by using a solder 52. Thus, the L-shaped leads 21 and 22 are mounted on the principal su rface 11a of the printed board 11.
As described above, in the lead mounting method according to the embodiment of this invention, the flat lead is preliminarily formed into the L shape and thereafter mounted onto the principal surface 11a of the printed board 11. Therefore, as compared with the above-mentioned lead mounting method in which the flat lead is bent by 90° after soldering using the solder 50, it is possible to completely avoid occurrence of a crack in a soldering portion by the solder 50.
As illustrated in Fig. 3 which relates to a comparative example, the mounted part 21a has a length Lm substantially equal to a length LI of the land 50 in a bending direction.
In Fig. 3 which relates to a comparative example, the length LI of the land 50 is equal to the length Lm of the mounted part 21a. According to the invention, in order to more firmly attach the lead, the length Lm of the mounted part 21a is slightly shorter than the length LI of the land 50 so as to form a fillet.
In the foregoing embodiment, the nickel lead is used as the lead. However, the material of the lead is not limited to nickel. Further, in the foregoing embodiment, description has been directed to the lead mounting method in which the lead is electrically connected to the terminal (the anode terminal or the cathode terminal) of the secondary battery.

Claims

A lead mounting method of mounting, onto a principal surface (11a) of a
printed board (11), a lead adapted to be connected to a terminal of a secondary battery, characterized in that said method comprises the steps of:
preparing a flat lead which has a mounted part (21 a, 22a) having a lower surface to be disposed on the principal surface (11a) of said printed board (11) and a connected part (21b, 22b) to be connected to said terminal;

bending said flat lead into an L-shape so that said mounted part (21 a, 22a) and said connected part (21b, 22b) are perpendicular to each other to obtain an L-shaped lead (21, 22); and

connecting and fixing the entire lower surface of the mounted part (21 a, 22a) of said L-shaped lead (21, 22) to a land (50) formed on the principal surface (11a) of said printed board (11) by soldering (52) so that the mounted part of said L-shaped lead has a length (Lm) in a bending direction slightly shorter than a length (LI) of the land (50) and so as to form a fillet of the soldering.
A lead mounting method as claimed in claim 1, wherein said lead is a nickel lead.